A drawworks is a common piece of oil field equipment that is used in oil and gas drilling and production. A drawworks is typically mounted near an oil rig. A common function of a drawworks is to raise and lower drill pipe and casing out of and into a wellbore. A drawworks can be referred to as a hoist or a winch. There are many different sizes of drawworks that are used in the drilling and mining industries. The sizes of the drawworks are reflected in the power ratings for such drawworks. These drawworks share similar operating modes and similar equipment.
Drawworks are used in the hoisting and lowering of loads, such as drill pipe, when inserting and extracting the drill pipe into and out of the open well. The extraction of the pipe can require extracting in excess of 30,000 feet of pipe in order to change drill bits or tooling during the drilling operation. During typical oil well drilling operations, the drill pipe is often hoisted and lowered many times.
During mining operations, similar equipment is used in hoisting coal, overburden material, sand and gravel, phosphates and other minerals. These are just a few of the typical operations in which the drawworks are utilized. In mining operations, a bucket is often lowered for the purposes of allowing the loading of the bucket with the materials. After the bucket is loaded, the drawworks is used so as to hoist the loaded bucket to an elevation whereby the bucket is unloaded at a location above the earth.
FIG. 1 shows a conventional drilling rig 10 that utilizes a prior art drawworks 26. The drawworks 26 is mounted to the rig floor 12 within the interior of the oil derrick 11. The drawworks 26 has a wire line 24 extending around the pulley 25 so as to raise and lower drill pipe 14 from and to the wellbore 16. The pulley 25 is also known as a crown block. The wellbore 16 is formed in the earth 50. The drill pipe 14 can be a drillstring that is a series of drill pipes extending within the wellbore 16 in the earth 15. Individual drill pipe 14 is connected to the drillstring at threaded joint 17. Portions of the drillstring may have stabilizer portions that include stabilizer elements 18 that extend helically along the outer surface of the pipe 14 so as to engage the wall of the wellbore 16 in a manner that centers the pipe 14 therein.
The drawworks 26 extends and retracts wire line 24 over the pulley 25 that is mounted on the oil derrick 11 so as to raise and lower the drilling unit 19 that holds the drillpipe 14. The line 24 is connected to traveling block 23. The traveling block 23 is suspended and moved upwardly and downwardly by the line 24 which is extended and retracted by the drawworks 26. The traveling block 23 is connected to the drilling unit 19. The drilling unit 19 has a swivel 22 at its upper end to which drilling fluid is introduced into the drill pipe 14, and by which the drilling unit 19 is suspended from the traveling block 23. The drilling unit 19, pipe handler 21, and the associated connected parts move vertically along axis 20. The vertical movement is guided by two vertical guide rails 27, or tracks, that are rigidly attached to the derrick 11. The drilling unit 19 is attached to a carriage 28. The carriage 28 has rollers that engage the rails 27. The rails 27 guide the carriage 28 for vertical movement upwardly and downwardly along the rails 27 parallel to vertical axis 20. The drill pipe 14 is inserted into and removed from the wellbore 16 through the wellhead 13.
The drawworks 26 typically has a hollow drum, a shaft that connects the drum to a motor, a transmission positioned between the motor and the drum, and a braking system for slowing the rotation of the drum. The drawworks 26 is mounted on the floor 12 of the drilling rig 10. The longitudinal axis of the drum and shaft is parallel to the drill floor 12. Typical motors used on the drawworks 26 are AC electric motors, DC electric motors, and diesel combustion engines. Power is typically transmitted from the motor to the shaft by a chain transmission mechanism or a gear transmission mechanism. The braking system can use a variety of techniques for braking the drum. The braking system can use disc brakes, band brakes, water-cooled brakes, or electric brakes. As the line 24 is retracted by the drawworks 26, the line 24 is wrapped around the drum of the drawworks 26. The wrapping of the line 24 around the drawworks 26 is similar to wrapping a thread around a spool.
The use of a transmission causes many problems commonly associated with the typical drawworks. A transmission is costly, adds weight to the drawworks, and needs periodic repair. Maintenance of a transmission can be costly, especially in the event of a total failure of the transmission. Power is also lost with the use of a transmission due to frictional forces that are inherent in the use of transmissions. Typical drawworks 26 also use large amounts of energy for changing the direction of rotation of the drawworks 26. Thus, there is a need for a simple design of a drawworks that is lighter, easier to maintain, uses less energy, and is more energy efficient.
In the past, various patents have issued relating to drawworks. For example, U.S. Pat. No. 6,182,945, issued on Feb. 6, 2001 to Dyer, et al., discloses a fully redundant drawworks with two complete and totally independent systems for controlling and powering the drum and the drum shaft of the drawworks. Each system has at least one power source, a power transmission, and a coupler connected to the power source and to the transmission and to the drum shaft. Each system has a braking system, such as disc brakes, band brakes, electric brakes, or water-cooled brakes. In the event that any component of either system fails, the fully redundant drawworks has the ability to raise drillpipe from a wellbore so as to avoid the risk of a “stuck” drill pipe.
U.S. Pat. No. 4,226,311, issued on Oct. 7, 1980 to Johnson et al., discloses a disc-type brake apparatus adapted for installation in combination with the drawworks of a wellbore drilling operation. The apparatus automatically senses any reverse torque situation in the drill pipe and quickly sets the brake for precluding transmission of any reverse torque to the rotary table device clutch mechanism therefor.
U.S. Pat. No. 3,653,636, issued on Apr. 4, 1972 to Burrell, discloses a reversible hydraulic motor and a high-pressure/low-pressure hydraulic reservoir system that are used to counterbalance the weight of a drillstring or other well equipment suspended from a line wound on a drawworks positioned on a floating vessel. A load cell controls the torque output and the direction of the output drive of the hydraulic motor. Upon downward movement of the floating vessel, high pressure hydraulic fluid from an accumulator moves through the hydraulic motor into a low pressure hydraulic fluid reservoir to provide increased torque to the drawworks as the drawworks spools a wire line upward. Upon an upward movement of the floating vessel, the hydraulic motor reverses so as to move low pressure fluid from the low pressure reservoir to the high pressure accumulator. This decreases torque and reverses direction to the drawworks as the drawworks extends the line.
U.S. Patent Publication No. 2008/0116432, published on May 22, 2008 to Folk et al., discloses a winch that includes an electric motor having a fixed stator, and a cylindrical rotor which rotates about the stator. A drum is affixed to the rotor and carries a cable which is wound or unwound by the winch. The winch may be a drawworks for an oil rig. The electric motor can be a permanent magnet electric motor. A bearing mechanism is positioned between the motor stator and the motor rotor.
U.S. Pat. No. 3,211,803, issued to Pryor et al., discloses a generator-feed electric drive for a drawworks that has electric motors, a driving connection between the motors and the drawworks, a generator, an electrical connection to the generator and the motors for supplying electricity to the motors, an engine, and a connection between the engine and the generator for supplying power to the generator. The electric motors have a total power absorption capacity that is substantially larger than the power output capacity of the engine, whereby the torque available to drive the drawworks is substantially greater than would be available from motors having a total power absorption capacity equal to the power output capacity of the engine.
U.S. Pat. No. 4,438,904, issued on Mar. 27, 1984 to White, discloses a drawworks that has a drilling platform supporting the drawworks, a cable-drum shaft rotatably supporting the cable drum between two upright support-wall members, an input shaft, a driving mechanism for driving the input shaft in rotation, a clutch-controlled chain sprocket and chain transmission for causing rotation of the drum shaft and the cable drum at any of multiple speeds in response to rotations of the input shaft, and a controller disposed outside of one of the support-wall members. The drum shaft has an extension beyond one of the support-wall members. A single outboard brake is fixed to the drum-shaft extension.
U.S. Pat. No. 6,029,951, issued on Feb. 29, 2000 to Guggari, discloses a system and method for the use of a drawworks where the drawworks has a rotatable drum on which a line is wound. The drawworks and the line are used for facilitating a movement of a load suspended on the line. A drawworks-control system monitors and controls the drawworks. A brake arrangement is connected to the rotatable drum for limiting the rotation of the rotatable drum. An electrical motor is connected to the rotatable drum for driving the rotatable drum. The drawworks control system provides a signal that is representative of the calculated torque value of the electrical motor wherein pre-torquing is generated in the electrical motor in response to the signal. Control of the rotation of the rotatable drum is transferred from the brake arrangement to the electrical motor when the electrical motor pre-torquing level is substantially equal to the calculated torque value.
U.S. Pat. No. 4,046,355, issued on Sep. 6, 1977 to Martin, discloses a control apparatus for use with a drawworks assembly that has a work piece suspended from, and applying tension to, a cable. One end of the cable is wound on a drum. The rotation of the cable is controlled by a power brake mechanism. The control apparatus has a cable tension sensor that produces a tension signal proportional to the tension in the cable. A pulse generator produces a pulsed control signal. A brake control applies the tension signal to the power brake mechanism in response to the control signal.
U.S. Patent Application No. 60/726,077, filed on Oct. 13, 2005 by the present inventor, discloses a drawworks for drilling and mining operations. The drawworks has a wire rope drum which is driven by at least one AC motor. A drive shaft couples a brake with the wire rope drum. The motor is operated from a utility power supply. The drawworks has a flywheel system that stores energy while braking the rotation of the wire rope drum of the drawworks. Energy stored in the flywheel is used to begin another rotation of the wire rope drum.
When drawworks are used in the drilling of oil and gas well, the speed of the drawworks will vary dependent on the weight of the load. For heavy loads, where the torque demand is high, the required speed of hoisting or lowering the load (pipe) is low. For an empty block or for very light loads (e.g. short pipe lengths), the required speed increases. As such, it would be desirable to have a permanent magnet motor associated with the drawworks that could have a high speed and a low speed. Such a high speed and a low speed, under constant power conditions, could provide either enhanced torque or reduced torque depending upon the requirements of the load.
In the past, patents have issued relating to permanent magnet motors. For example, U.S. Pat. No. 4,910,790, issued on Mar. 20, 1990 to P. A. Kerashaw, shows a two-speed permanent magnet D.C. electric motor. This D.C. electric motor has a housing, permanent magnets carried by the housing, and an armature assembly installed in the housing. The armature assembly has a shaft rotatably mounted in the housing, first coil windings, a first commutator connected to the first coil windings, second coil windings and second commutator connected to the second coil windings. A first set of brushes is carried by the housing and engages the first commutator for applying a D.C. voltage to the first coil windings to cause rotation of the armature assembly at a first speed. A second set of brushes is carried by the housing and engages the second commutator for applying the same D.C. voltage to at least the second coil windings to cause rotation of the armature assembly at a second speed.
U.S. Pat. No. 5,952,757, issued on Sep. 14, 1999 to J. H. Boyd, describes a line start permanent magnet motor. This motor has a stator with a stator core, a start winding, and first and second main windings. The first main winding and the start winding are configured to form a lower number of poles than the second main windings. The stator core forms a stator bore. The motor also includes a rotor having a rotor shaft concentrically arranged axially of the stator core and a rotor core positioned concentrically with the rotor shaft. Secondary conductors are arranged axially of the rotor shaft and extend through the rotor core. A plurality of permanent magnets are located at an outer periphery of the rotor core and are magnetized to form a number of poles equal to the number of poles formed by the second main winding.
Additionally, where permanent magnet motors would be used for the direct drive of the drawworks, it is important to be able to avoid the adverse effects of a sudden loss of power. Due to the fixed field flux inherent in permanent magnet motors, when there are overhauling loads and the AC mains are disconnected, no power is applied to the windings of the motor. As such, a “runaway condition” due to the overhauling load of a weight being suspended in free, open air can occur. This can result in a crash of the heavy load freely falling via weight and the earth's gravity. As such, damage can occur and safety concerns can arise for rig personnel. As such, a need has developed whereby the permanent magnet motor can be made inherently safe so as to avoid any such “runaway conditions”.
It is an object of the present invention to provide a direct-drive drawworks.
It is another object of the present invention to provide a drawworks that requires no gearing mechanism.
It is another object of the present invention to provide a drawworks that has a very high power density.
It is another object of the present invention to provide a drawworks that is relatively light weight.
It is still another object of the present invention to provide a drawworks that can be easily transported on conventional road systems.
It is another object of the present invention to provide a drawworks which has minimal assembly requirements in the oil field.
It is another object of the present invention to provide a drawworks that is easily replaceable in the oil field.
It is still another object of the present invention to provide a drawworks that has reduced inertial effects.
It is another object of the present invention to provide a drawworks that reduces costs of operating and repair.
It is a further object of the present invention to provide a permanent magnet direct drive drawworks in which the permanent magnet motor can be operated at a high speed or a low speed.
It is still another object of the present invention to provide a permanent magnet direct drive drawworks that allows the speed of the motor to be adapted to various load conditions affecting the drawworks.
It is still another object of the present invention to provide a permanent magnet direct drive drawworks which effectively prevents any runaway conditions from occurring because of an overhauling load or a loss of power.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.